The inventors are familiar with systems for plotting the trace of a pencil or of an eraser on a writing medium comprising:
a magnetic ring suitable for being fixed removably onto the pencil or the eraser,
a network of magnetometers suitable for measuring the magnetic field generated by the magnetic ring, this network of magnetometers being fixed with no degree of freedom to a bearing face of a tablet, this bearing face forming the writing medium or supporting the writing medium,
a computer suitable for determining the position and the orientation of the magnetic ring in order to deduce therefrom the position of the tip or point of the pencil or of the eraser relative to the bearing face from the measurements of the network of magnetometers.
Such a system is described in the patent applications filed under the numbers FR1252881 and FR1252880 on 29 Mar. 2012.
This system presents the notable advantage, compared to other known systems, that the pencil or the eraser only needs to be equipped with a magnet to be able to work.
The term “pencil” is used here to describe any utensil that can be directly manipulated by the hand of a human being in order to draw a trace on a physical writing medium, such as, for example, a pen or a brush. Typically, the trace is visible to the naked eye either directly on the physical medium or on a display screen. To leave a directly visible trace on the medium, the pencil deposits a colored liquid or solid to form the trace that is directly visible to a human being on the writing medium. The colored liquid is typically an ink or paint. The colored solid is, for example, graphite.
The term “eraser” is used here to describe any utensil that can be directly manipulated by the hand of a human being in order to draw a trace on a physical writing medium which, when it encounters the trace left by the pencil, erases the trace left by this pencil. The erasure can be a digital erasure of data of a trace recorded using a pencil or be a physical erasure of the trace on the medium. For example, the physical erasure of the trace on the medium can be caused by a chemical reaction and/or a mechanical effect such as abrasion. Unlike the pencil, the trace drawn by the eraser is not generally visible to the naked eye.
The term “draw” is used here to encompass the act of running a point over the writing medium in order to write or erase.
The writing medium is a sheet of paper, a canvas or any other medium on which it is possible to draw.
To obtain a good accuracy in the plotting of the trace of the pencil or of the eraser, the latter must be equipped with a magnetic ring exhibiting a powerful magnetic field. This dictates the use of particular magnetic materials which exhibit, generally, a very high hardness. Thus, the magnetic rings produced with such a magnetic material have a predefined internal diameter which cannot be adapted to different pencils or erasers that have different external diameters. This therefore dictates the production of specific pencils or erasers that have an external diameter corresponding to the internal diameter of the magnetic ring.
However, it is desirable to enable the user to use the trace plotting system with his or her usual pencils or erasers. These usual pencils or erasers exhibit a wide diversity of forms and notably of external diameters of the body of the pencil or of the eraser. This diversity of external diameters is incompatible with the rigidity of the magnetic magnet which has to be used in the plotting system. Thus, the current plotting systems do not make it possible to use pencils or erasers of different external diameters.
Prior art is also known from: EP0159498 A1, W02008/070147A1, US2011/086335A1, W02005/024620A1, FR2586302A1 and FR2952450A1.